A train wheel is subject to normal wear due to friction contact between the wheel and the rail. As a train wheel wears out, the rim thickness and flange thickness decrease and the flange height increases. Thus, there is a need to accurately measure the rim thickness, flange thickness, flange height, wheel reference groove, wheel diameter, flange throat profile (i.e., a collection of two or more measurement point data acquired in the area of interest), and wheel "Gage" in order to ensure that wheels in operation are safe. These safety check measurements typically take place in train yards and in train shops. Before the train can leave the yard, all the wheels are visually inspected and a wheel with noticeable wear is measured to verify that the wheel is in good condition. Also, train wheels are inspected on a routine basis to verify that the wheels are in good condition.
Similar measurements are used in recutting (wheel truing) the wheels to restore wheel profile as wheel wear exceeds certain permissible tolerances of flange height and flange thickness. This wheel truing operation takes place in train shops. Locomotives, freight and transit cars are typically rolled into the shop for possible wheel repair work. Also, similar measurements are used by wheel manufacturers for production quality control of train wheels as the wheels roll off a production line.
Historically, these measurements have been manually taken using mechanical calipers. One such widely used mechanical wheel gauge looks like an inverted "J". In use, the readings are read and recorded by the operator directly off the mechanical gauge while the gauge is positioned against a wheel. There are several drawbacks, however, to such a mechanical gauge for the above-mentioned applications. In a situation where the wheel is installed on a train, for example, there are three major problems. First, the train wheel has quite a few mechanical parts such as brakes, shock absorbers and axle support mechanisms around it. Measurements have accordingly been difficult to take with the mechanical gauge because of the limited space around the wheel and because of the location of the flange on a train wheel (towards the inside of a track). Secondly, environmental conditions where the measurements are made are often poor. For example, dim light often makes this task extremely difficult to perform. Thirdly, measuring a number of wheels can be laborious.
Further, operator dependent manual recording errors of measurement(s), and keypunch errors, make this important wheel wear monitoring process on installed wheels very undependable. Measurement error can lead to three problems for the railroad. First, unacceptable wheels can remain in service providing an uncomfortable ride and posing a significant safety and liability hazard; second, wheels can be condemned which should be trued or reprofiled; and third, wheels which should be condemned are sometimes sent for trueing, resulting in a disruption of the work flow in the wheel trueing shop.
The mechanical gauge has been in use since 1923. Nevertheless, every year a number of train accidents are attributed to excessively worn-out wheels. Train maintenance staff measurement errors contribute to this safety risk. Several companies have invested heavily in computerized wheel management systems which are designed to automate the wheel maintenance process. However, the current mechanical gauge does not provide accurate measurements to feed to such computerized wheel management systems. Furthermore, the wheel maintenance staff cannot restore a wheel to a prescribed profile when accurate wheel wear measurements are unavailable.
Several attempts have been made to automate the wheel wear measurement process. These attempts include handheld gaging systems and track mounted gaging systems. Among the handheld gaging systems, one arrangement is featured in U.K. Patent Application No. GB 2183840A (granted Jun. 10, 1987, Martti Kurkinan, inventor). This arrangement measures only rim profile using an electro-mechanical contact probe which travels across the rim. Measured profile is compared with a good reference profile gathered using a second probe. Another attempt is featured in U.S. Pat. No. 4,904,939 (granted Feb. 27, 1990, Zahid Mian, inventor). This approach addresses the typical problems with handheld railway wheel profile measurement arrangements such as non-portability, inability to gather vital measurements, and significant mechanical wear of the instrument. However, two difficulties remain. One is that the wheel measurement process remains laborious when many wheels have to be measured quickly. Second is that accessing mounted wheels is still not always easy due to the presence of other mechanical parts such as brake shoes surrounding a mounted wheel.
Several other efforts have been made in the area of track mounted wheel measurement systems, for example, reference U.S. Pat. No. 3,820,016 (granted Jun. 25, 1974, Marion Giesking, inventor) and U.S. Pat. No. 4,407,072 (granted Oct. 4, 1983, Hoskins, inventor). Both of these arrangements utilize complicated electromechanical parts which come in contact with the wheel. Therefore, these arrangements necessarily lack accuracy, result in wear of measurement mechanisms over time, and are difficult to maintain.
Another arrangement is mentioned in European patent No. EP 0007227A1 (W. H. Steel, et al., inventors). This arrangement suggests using a high intensity light source and a TV camera to gather information about rail-head image primarily. The approach has several deficiencies, however; namely: it is vulnerable to ambient light conditions producing erroneous measurements; it requires time consuming image processing for each image acquired; it does not correct for image distortion due to relative movement between the arrangement and the camera; and it does not provide the necessary wheel dimensions such as flange thickness.
Still another arrangement is described in U.S. Pat. No. 4,798,963 (granted Jan. 17, 1989, Wittkopp, inventor). This arrangement provides only a wheel diameter measurement using multiple light sources. Unfortunately, the method is susceptible to ambient light conditions, and does not correct for measurement errors due to sideways movement of the wheel. A similar arrangement is described in U.S. Pat. No. 4,798,964 (granted Jan. 17, 1989, Schmalfuss, inventor). Based on optical measurement schemes, this arrangement uses multiple broad band light sources, a mechanical platform subject to wear, and complex optical means to measure wheel diameter and tread surface. Unfortunately, this system is difficult to keep clean of dirt in the railway environment, provides questionable measurement accuracy, operates at very low speeds due to a complicated mechanical arrangement, does not provide wheel dimensions in absolute units, is expensive to produce due to complex optical measuring schemes, requires significant installation space, and is not suitable for outdoor operation. Similar to other camera-imaging based systems, the system relies on acquiring a complete image of the wheel, requiring slow and expensive image processing hardware that does not provide direct wheel measurements.
Therefore, there presently exists a genuine need for a track mounted electronic train wheel non-contact gaging system capable of improving the integrity of the wheel wear measurement process by quickly gaging key dimensions of the wheel irrespective of lateral and horizontal wheel movement. Such a system will provide accurate and quick wheel wear measurements in absolute units automatically, and directly thus reducing the opportunities for operator errors. Featuring high speed response, easy maintenance, minimal wear over time, minimal in field maintenance, low cost, and the capabilities of directly feeding the maintenance computer with wheel wear information, such a system will find use in a railway repair shop, railway yard, main railway service track, and railway wheel production facilities.